Innate immunity and macrophages (MFs) contribute to the development and pathophysiology of hypertension. Knowledge gaps exist for the cellular and molecular mechanisms in MFs that contribute to hypertension. We identified a single gene, Alox15, that is crucial in 3 models of hypertension. Alox15 encodes 12/15-lipoxygenase (12/15-LO) that metabolizes arachidonic acid to hydroxyeicosatetraenoic acids (HETEs). An important role for MF 12/15-LO in hypertension was identified by differentially excluding MF and non-MF sources of 12/15-LO by: (1) Depletion of MFs (and thus MF 12/15-LO) in wild type (WT) mice prevents hypertension. (2) Global deletion of the Alox15 gene (Alox15-/-) prevents hypertension. (3) Transfer of 12/15-LO-containing WT MFs to these Alox15-/- mice restores hypertension. (4) Bone marrow cell-specific Alox15 deletion prevents hypertension. Also, MFs accumulate in arteries and polarize to the M1 (pro-inflammatory) phenotype, but not M2 (anti-inflammatory) phenotype, with hypertension in WT mice but not in Alox15-/- mice. Thus, 12/15-LO regulates MF M1 polarization in hypertension. These results indicate the need to understand the contributions of MF 12/15-LO to hypertension. The objective of this proposal is to define the role of 12/15-LO and its metabolites as a common pathway to hypertension through regulation of the pro- and anti-inflammatory pathways of innate immunity. The central hy- pothesis is MF 12/15-LO and its HETE metabolites regulate MF accumulation, phenotype and cytokine release that activate pro-hypertensive mechanisms in the vasculature and kidneys resulting in hypertension. (1) We will use MF-targeted deletion of Alox15 to establish the crucial role of MF 12/15-LO in regulating immune, vascular and renal pro-hypertensive mechanisms. The working hypothesis is that MF 12/15-LO stimulates MF accumu- lation, polarization and cytokine release in arteries, kidneys and brain that contribute to hypertension by activat- ing vascular and renal mechanisms to enhance constriction, inhibit dilation, promote renal injury and decrease sodium excretion.!(2) The in vivo effects of HETEs on hypertensive mechanisms are unknown. Blockade of HETE synthesis in Alox15-/- mice will be bypassed by administering exogenous HETEs to restore hypertension. The working hypothesis is that 12- and 15-HETE stimulate immune, vascular and renal mechanisms that restore hypertension in Alox15-/- mice. (3) The importance of MF polarization and its regulation by 12/15-LO in hyper- tension will be defined. To determine if Alox15 deletion prevents hypertension by redirecting MF polarization, in vivo and in vitro methods will be used to polarize M0 MFs to the M1 or M2 phenotype, and the 3 phenotypes evaluated for restoration of hypertension in MF-depleted mice. The working hypothesis is that 12/15-LO directs MF polarization to M1 phenotype, and M1, but not M2, MFs promote hypertension. The expected outcomes will advance the field by identifying a new molecular mechanism involving the 12/15-LO-HETE pathway that broadly regulates the participation of MFs and innate immunity in hypertension by specifying the M1 MF phenotype that contributes to hypertension and by mediating vascular and renal pro-hypertensive activities of MFs.